A new concept for solar energy thermal conversion

A material has been developed which allows a new approach to be made to the conversion of solar energy to heat. It consists of a dense array of metal whiskers grown with spacings of a few wavelengths of visible light. The material selected has low emissivity, and achieves significant optical absorption by trapping the light by a geometric maze effect. We have deomonstrated that absorption of normal incidence light is greater than 98% from 0.5 to 40-μm wavelengths, and hemispherical emissivity at 550°C can be made less than 0.26. Since surfaces can be made of a single refractory element, such as W, high-temperature solar conversion (550°C) should be maintained with good surface stability.